This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-283533, filed on Sep. 18, 2001; the entire contents of which are incorporated herein by reference.
The present invention relates to an electrostatic microactuator, a method of activating the same, and a camera module used with the same, and more particularly, it relates to an electrostatic microactuator electrostatically powered, assembled easily, and having improved smoothness, stability, and reliability in actuation, a method of activating such an electrostatic microactuator, and a camera module used with the same.
For recent years, a miniaturized linear actuator of more downsized design, precise operation and reduced cost has been increasingly needed for focal adjustment of a super-compact camera, for example. An example of a solution to such needs is an electrostatic actuator disclosed in Japanese Patent Laid-Open Publication H08-140367.
FIG. 27 is a schematic diagram showing a structure of the prior art electrostatic actuator.
As shown in FIG. 27, an electrostatic actuator 101 is comprised of a movable piece 102 and a couple of statical members 103a and 103b overlaid on the opposite sides of the movable piece. The statical members 103a and 103b have their respective two groups of branch pads connected to electrodes, and there are four groups of branch pads connected to electrodes A to D for the couple of the upper and lower statical members.
Branch pads in the statical members 103a and 103b, which are connected to corresponding ones of the electrodes A to D, are arranged at the same pitch with branch pads 104 of the movable piece 102, and all the branch pads are the same in width in both the statical and movable pieces. In the static pieces 103a and 103, however, the branch pads separately correlated with two of the electrodes (e.g., electrodes A and C) are alternately placed in an interlacing deployment. In addition to that, the branch pads of the upper and lower static pieces 103a and 103b are correlated with one another in a xc2xd out-of-phase pattern where the upper branch pads are deviated by a half of their respective width from their counterparts or the lower branch pads.
Applying high voltage to the electrode A, an electrostatic force (Coulomb force) developed between the electrode A and the branch pads 104 correlated with an electrode E causes the movable piece to be attracted by the upper statical member 103a (toward a position where the branch pads correlated with the electrodes A and E are aligned in phase). Then, switching the electrode supplied with the high voltage to the electrode B, the movable piece 102 is attracted by the lower statical member 103b (toward a position where the branch pads correlated with the electrodes B and E are aligned in phase). In this ways the succeeding switching of the electrodes as in a manner of A to B, B to C, C to D, and so forth enables the movable piece 102 to microscopically vertically vibrate and macroscopically laterally move (e.g., move to the right in FIG. 27 with one degree of freedom).
Supplying the high voltage to the electrodes in the reversed order as in A to D, D to C, C to B, and so forth enables the movable piece to move to the left in FIG. 27.
To implement such a way of the motion, the vertically juxtaposed statical members 103a and 103b must be under accurate control of the phases or the branched-electrode pattern, and the movable piece 102 must also have an accurately fabricated electrode pattern on both the opposite sides. This requires time consuming and complicated assembling task and accordingly leads to a cost increase, which are some of problems that must be overcome for a mass-production of such a high precision actuator.
Further, since the movable pieces in this electrostatic actuator vibrates with a relatively large amplitude between the juxtaposed statical members 103a and 103b to laterally move pitch by pitch, its microscopic movement is not satisfactorily smooth, and it is desirable to improve both the physical and operational mechanisms of the actuator.
The present invention is made to address the aforementioned disadvantages in the prior art. Accordingly, it is an object of the present invention to provide an electrostatic actuator that can be easily assembled and suitably mass-produced and that can implement requirements of both the steady, smooth and stable operation and the enhanced reliability, a method of activating the same, and a camera module used with the same.
According to an embodiment of the present invention, there is provided an electrostatic actuator comprising: a first statical member having an electrode array being comprised of at least three groups of activating electrodes periodically deployed in a first direction; a second statical member faced to the first statical member and having an electrode extending in the first direction; a movable piece provided between the first and second statical members, and a switching circuit applying a first voltage to cause a potential difference between at least one of the groups of the activating electrodes and the movable piece and also applying a second voltage to cause a potential difference between the electrode of the second statical member and the movable piece, the first voltage being applied to sequentially switch a destination of applied voltage from at least one of the groups of the activating electrodes to another in the first direction, the second voltage being intermittently applied while the first voltage is applied.
According to an anther embodiment of the present invention, there is provided an electrostatic actuator comprising: a first statical member having an electrode array being comprised of at least three groups of activating electrodes periodically deployed in a first direction; a second statical member faced to the first statical member and having a first electrode extending in the first direction and a second electrode extending in the first direction in almost parallel with the first electrode; a first movable piece provided between the first and second statical members, a second movable piece provided between the first and second statical members, and a switching circuit applying a first voltage to cause a potential difference between at least one of the groups of the activating electrodes and the first movable piece and also applying a second voltage to cause a potential difference between the first electrode and the first movable piece, the first voltage being applied to sequentially switch a destination of applied voltage from at least one of the groups of the activating electrodes to another in the first direction, the second voltage being intermittently applied while the first voltage is applied, and the switching circuit applying a third voltage to cause a potential difference between at least one of the groups of the activating electrodes and the second movable piece and also applying a fourth voltage to cause a potential difference between the second electrode and the second movable piece, the third voltage being applied to sequentially switch a destination of applied voltage from at least one of the groups of the activating electrodes to another in the first direction, the fourth voltage being intermittently applied while the third voltage is applied.
According to an anther embodiment of the invention, there is provided a camera module comprising: a imaging device; a electrostatic actuator, the electrostatic actuator including: a first statical member having an electrode array being comprised of at least three groups of activating electrodes periodically deployed in a first direction; a second statical member faced to the first statical member and having an electrode extending in the first direction; a movable piece provided between the first and second statical members, and a switching circuit applying a first voltage to cause a potential difference between at least one of the groups of the activating electrodes and the movable piece and also applying a second voltage to cause a potential difference between the electrode of the second statical member and the movable piece, the first voltage being applied to sequentially switch a destination of applied voltage from at least one of the groups of the activating electrodes to another in the first direction, the second voltage being intermittently applied while the first voltage is applied; and a lens mounted on the movable piece of the electrostatic actuator and inputting a optical information to the imaging device.
According to an anther embodiment of the invention, there is provided a camera module comprising: a imaging device; a electrostatic actuator including: a first statical member having an electrode array being comprised of at least three groups of activating electrodes periodically deployed in a first direction; a second statical member faced to the first statical member and having a first electrode extending in the first direction and a second electrode extending in the first direction in almost parallel with the first electrode; a first movable piece provided between the first and second statical members, a second movable piece provided between the first and second statical members, and a switching circuit applying a first voltage to cause a potential difference between at least one of the groups of the activating electrodes and the first movable piece and also applying a second voltage to cause a potential difference between the first electrode and the first movable piece, the first voltage being applied to sequentially switch a destination of applied voltage from at least one of the groups of the activating electrodes to another in the first direction, the second voltage being intermittently applied while the first voltage is applied, and the switching circuit applying a third voltage to cause a potential difference between at least one of the groups of the activating electrodes and the second movable piece and also applying a fourth voltage to cause a potential difference between the second electrode and the second movable piece, the third voltage being applied to sequentially switch a destination of applied voltage from at least one of the groups of the activating electrodes to another in the first direction, the fourth voltage being intermittently applied while the third voltage is applied; a lens mounted on the first movable piece of the electrostatic actuator and inputting a optical information to the imaging device; and a lens mounted on the second movable piece of the electrostatic actuator and inputting a optical information to the imaging device.
Appropriately configured according to the present invention, a movable piece, while being attracted and almost fitted onto a surface that has branch pads connected to a first electrode, is permitted to move, thereby restraining vertical vibration under strong attractive force, so as to attain the desired stable, smooth, and reliable operation.